'Prosecution criteria'

It says the nature of the investigation was "wholly disproportionate and unjustified having regard to the Twitter material itself and the broader circumstances of the case".

Miss Brown was appointed to the youth post on 3 April, when she was still 16, by Kent Police and Crime Commissioner Ann Barnes to represent young people across the county.

The Mail on Sunday later reported Ms Brown had boasted about her sex life, drug-taking and drinking on her Twitter account @vilulabelle and had also posted violent, racist and anti-gay comments. The account has since been removed.

Kent Police said in a statement: "Officers must first determine the extent of the misuse of social media so that the Crown Prosecution Service can then determine whether or not any potential evidence meets the set criteria for a prosecution.

"We will investigate all complaints thoroughly but cannot comment further on the progress of a live investigation."